Offretite synthesis from minerals

ABSTRACT

A synthetic offretite having a capacity for sorbing benzene and other large molecules is prepared from an aqueous nutrient containing tetramethyl ammonium hydroxide, potassium hydroxide, and a suitable mixture of reactive aluminosilicate minerals, usually comprising sorptive silica.

United States Patent [1 1 Flank Sept. 11, 1973 [52] U.S. Cl. 252/455 Z,423/118, 423/329 [51] Int. Cl B0lj 11/40 [58] Field of Search 252/455 Z;

[56] References Cited UNITED STATES PATENTS 3,578,398 5/1971 Jenkins23/113 3,341,284 9/1967 Young 23/112 R 3,436,174 4/1969 Sand 23/1133,314,752 4/1967 Kerr 23/113 Primary Examiner-C. F. Dees Att0meyJohn R.Ewbank and R. Max Klevit [57] ABSTRACT A synthetic offretite having acapacity for sorbing benzene and other large molecules is prepared froman aqueous nutrient containing tetramethyl ammonium hydroxide, potassiumhydroxide, and a suitable mixture of reactive aluminosilicate minerals,usually comprising sorptive silica.

3 Claims, No Drawings 1 OFFRETITE SYNTHESIS FROM MINERALS BACKGROUND OFINVENTION 1. Field of Invention This invention relates to crystallinezeolitic aluminosilicates synthesized in an alkaline medium containingreactive aluminosilicates derived from minerals such as clay or perlite.

2. Prior Art Zeolite T, as described in U.S. Pat. No. 2,950,952, ischaracterized by X-ray diffraction data corresponding essentially tothat of erionite which has small pore sorption characteristicsresembling those of Zeolite T.

The powder technique for X-ray diffraction of erionite and offretiteprovide data which are nearly identical. Geologists have debated whetherany alleged differences between erionite and offretite were structuralor semantic. Bennett and Gard, in a letter to Nature, volume 214, page1005 (June 3, 1967), clarified the structural difference by pointing outthat a staggering of building block components accounted for the smallpore size in the erionite structure, whereas offretite was completelyfree from any staggering, and had large pores. Zeolite T was describedas being a disordered intergrowth of erionite and offretite." ThisNature lette'r explained why the use of X-ray powder techniques wasinadequate for distingushing samples of erionite and offretite and whysingle crystal techniques were necessary for distinguishing thestructures by X-ray diffraction. The letter indicated that the relationbetween erionite and offretite resembled that between gmelinite andchabazite. The presence of impurities and/or faulting in offretite wouldbe detectable by electron-diffraction streaking. The letter suggestedthat fully ordered offretite could possibly be synthesized by carefulchoice of experimental conditions. Such a synthetic product would havevaluable commercial applications. An article by Gard and Tait which waspresented at the Second International Conference on Molecular SieveZeolites at Worcester in September, 1970, further clarified theserelationships and described, among other things, their characterizationand identification of a sample of natural unfaulted offretite.

British Pat. No. 1,188,043, related to Rubin application Ser. No.717,977, filed Apr. 1, 1968 in the U.S. Patent Office, and assigned toMobil Oil Corp., describes a synthesis of an unfaulted offretite by thecontrolled aging of an aqueous alkaline system featuring sodiumhydroxide, potassium hydroxide and tetramethyl ammonium hydroxide,together with gelatinous alumina and gelatinous silicates. Although purechemicals are convenient for use in certain laboratory experiments, thecost of the pure siliceous chemicals and the pure aluminaceous chemicalsfor the synthesis of offretite tended to discourage commercialdevelopment of synthetic offretite. There has been a long standingdemand for a method of synthesizing large pore offretite frominexpensive sources of silica and/or alumina.

SUMMARY OF THE INVENTION In accordance with the present invention, analuminosilicate mineral is treated in a suitable manner (e.g., calciningto provide a reactive aluminosilicate, which is employed in a nutrientcomprising tetramethyl ammonium hydroxide and potassium hydroxide forconversion to fault-free offretite. Sorptive silica, such as obtained bycalcining diatomaceous earth, or derived for potassium silicate, isemployed to bring the SiO,/Al,0 unit mol ratio from that of the reactivemineral to a value near the magnitude of 20.

DESCRIPTION OF PREFERRED EMBODIMENTS The invention is clarified byreference to a plurality of examples.

EXAMPLE I A nutrient was prepared by mixing:

KOH(0.236 mol) 13.2g

(CH NOl-I-5l-1,O (0.1 mol) 18.3g

meta kaolin (0.02 mol) 4.4g

sorptive silica (0.4 mol) 23.7g

H 0 (5 mol) 90.0g

In the nutrient, some of the unit mol ratios were:

TA (total alkali)/Al,0;, 16.8

SiO /T A 1.31

SiO,/Al O 22.0

KOl-l/T A 0.7

Meta kaolin is prepared by calcining raw kaolin (alumino disilicatedihydrate) at a temperature removing substantially all of the hydratedwater. Sorptive silica powder is defined as silica powder having asufficiently large surface area to be readily soluble in aqueous alkali.The sorptive silica is desirably a calcined diatomaceous earth, butcertain varieties of raw (uncal cined) diatomaceous earth are capable ofdissolving in hot aqueous alkali (2 to 4 molar) to form alkali silicate(e.g., potassium trisilicate). Various types of sorptive silica are alsomarketed not as minerals, but as reactive silica. Pulverized silica gelhas acceptable solubility, as has a l-Ii-Sil brand of sorptive silica,comprising silica and water.

The nutrient was quiescently aged at 100C. for 3 days (72 hours) in aclosed container. The aged mixture was filtered to provide a crudeoffretite composition as the filter cake. After a thorough washing, thepurified offretite was dried and analyzed by X-ray diffraction, thusestablishing the presence of percent offretite in the product. The threemajor peaks of pure offretite provided the standards for thequantitative analysis of the offretite by X-ray diffraction.

The offretite in an aluminosilicate support was ionexchanged into thepredominantly ammonium form. Such supported ammonium offretite washeated in' a stream of vapor mixture of ammonia and steam attemperatures slowly rising to 600C. to provide an activated offretiteeffective in sorbing large amounts of cyclohexane, thus establishing thesubstantial freedom from erionite, Zeolite L, and/or other impurities.Minor amounts of any of several impurities destroy the large porecharacteristics of offretite, thus impairing its utility as a catalyst,sorbent for aromatic chemicals, and/or as a molecular sieve diffusionmembrane. The supported hydrogen 'offr'etite is advantageously employedas a hydrocarbon conversion catalyst for reactions such as dealkylationof alkyl aromatics, redistribution of- EXAMPLE II An aqueous nutrientwas prepared consisting of: KOH (0.23 mol) 13.2g

(Cl-l NOH-5l-l,O (0.1 mol) 18.3g Expanded perlite (0.02 mol A1 and 0.128mol SiO 11.1 g

Sorptive silica (0.299 mol) 17.6g

H 0 mol) 90.0g Perlite is a volcanic potassium sodium aluminosilicateglass containing about 17.4% A1 0 so that 588g of expanded perlitecontains 1 mol of A1 0 The expanded perlite was treated as if 588gcorresponded to a mol in A1 0, calculations. The expanded perlitecontained 69.5% SiO so that 86.5g corresponded to a mol in SiOcalculations.

KOH/(CH NOH 2.36

TAlAl O 17.7

SiO /TA 1.26

H O/TA 14.9

SiO /A1 0 22.2

(CH NOH/TA 0.3

KOl-l/TA 0.7 The expanded perlite and sorptive silica were dispersed inthe aqueous alkali by power stirring to provide a slurry which wastransferred to a sealed container for quiescent aging at 100C. for about3 days. The aged composition was dispersed in water, filtered, and thefilter cake washed and dried. The thus prepared powder contained 40percent offretite according to the standard analysis by intensity of thepeaks on X-ray diffraction. Thermal activation of the ammoniumexchangedpowder provided the large pore molecular sieve characteristics of asupported hydrogen offretite.

EXAMPLE lll Kaolin powder (catalytic grade substantially free from Fe oand containing small amounts of TiO,, was calcined briefly at about1,000C. to provide a product which when analyzed in Differential ThermalAnalysis instruments, had less than percent, desirably less than about 3percent, and usually less than 1 percent of the exotherm of metakaolin.The effects of 0.1 to 15 percent residual exotherm in de-exothermedkaolin upon reactivity with aqueous alkali have been clarified inprevious literature, which also emphasizes control of the calcination toprevent development of significant amounts of X-ray detectable mullitein the deexothermed kaolin.

An aqueous solution was prepared consisting of:

KOl-l (0.268 mol) 15g (Cl-l ).,NO1-l-5H O (0.11 mol) g H O (5.55 mol)100g Power stirring permitted dispersion of:

de-exothermed kaolin (0.0225 mol) 5.0g

hydrated (11 percent) sorptive silica (0.375 mol Si0 25.0g

to provide a batter-type slurry. The unit mol ratios for the nutrientwere:

KOl-l/(CH NOH 2.36

TA/Al O 16.8

SiO /TA 1.11

H OITA 14.7

SiO /A1 O 18.7

(CH ).,NOl-l/TA 0.3

KOl-l/TA 0.7 The batter was aged quiescently in a sealed container at100C. for 3 days to provide a product which, after washing and drying ofthe filter cake, contained 35 percent large pore offretite.

EXAMPLE IV A nutrient was prepared using the proportions and procedureof Example 1, but as a batch 10 times as large. The powdered offretiteproduct was ionexchanged 10 times in hot aqueous ammonium nitrate, andthe ion-exchanged powder was found to contain percent ammonium offretiteby X-ray diffraction.

Raw kaolin (19 parts) was blended with 1 part of the thus preparedsupported ammonium offretite. Water was added to provide an extrudatewhich was sliced into pellets. After steaming at 1,350F., the pelletswere tested as a cracking catalyst at CAT-D-l conditions (described inU.S. Pat. No. 3,455,842). A similar catalyst is prepared from kaolincontaining 4 percent ammonium ofiretite prepared from pure chemicals,and is employed as a control. Notwithstanding the high proportion ofinert kaolin diluent, the catalysts performed better than some of thecracking catalysts employed industrially shortly prior to theintroduction of supported crystalline cracking catalysts, as indicatedin Table 1.

TABLE 1 Control Example Vol.% gaso. 20.4 20.4 Wt.% coke 1.2 1.2 Wt.% gas6.9 6.9 Gas Gravity 1.33 1.33

By a variety of tests, the usefulness of the mineralderived supportedoffretite as a substitute for offretite derived from costly reagentgrade chemicals is established.

EXAMPLE V A hydrocracking catalyst was prepared by blending 2 parts ofraw kaolin and 1 part of the supported ammonium offretite of Example 1V,and slurrying the mixture in a 2.55 percent solution of Pd(NH;,) (NO,,)for 2 hours, drying the powder, and compressing the powder into pelletsin a tabletting press. The pellets were heated slowly in air to 900E.and then in a hydrogen stream to 1,050F. Analysis of the hydrocrackingcatalyst indicated 1 percent palladium and 30 percent hydrogenoffretite. The catalyst is highly effective in the hydrocracking of gasoil to gasoline.

By a series of tests, it is established that the following ranges of molratios should be maintained to achieve large pore offretite in theproduct.

Desirable Preferred The nutrient should be aged quiescently at atemperature within a range from 70 to 120C., desirably to 1 10C., andpreferably about C. for a period from about 1 to about 9 days, desirably2 to 4 days, and preferably for 3 days. The presence of an adequateamount of the (CH NOH is particularly important in attaining the largepore offretite structure and minimizing formation of Zeolite L, orerionite, or other impurities, small amounts of which convert theproduct into a structure having small or blocked pores. Theapproximately 1.5 molar concentration of the alkali trisilicate is alsoof significance, as is the presence in the nutrient of a larger unitratio of SiO /Al,0 than expected in the offretite product.

EXAMPLE VI An aqueous solution of a mixture of about 7 mols of potassiumtrisilicate K O-3SiO and about 3 mols of tetramethyl ammoniumtrisilicate is prepared in a concentration of about 15 moles oftrisilicate per liter, and the solution is heated to about 100C. Suchsolutions are desirably prepared by dispersing calcined diatomaceousearth in the hot aqueous alkali, followed by digestion and filtration,but other sources of sorptive silica may be employed.

Said solution of potassium tetramethyl ammonium trisilicate is employedas the solution in which a minor amount of calcined mineral isdispersed, aged for 3 days at 100C., and the recrystallized productrecovered by filtration. The recovered solids are washed, ion-exchangedwith ammonium nitrate, and calcined to provide a supported hydrogenoffretite having large pores adapted to sorb benzene. The calcinedminerals thus recrystallized into large pore offretite included:metakaolin (yielding product containing 80 percent offretite);de-exothermed kaolin (product containing 35 percent offretite); andperlite (product containing 40 percent offretite). Other calcinedalumino-silicates transformable into other zeolites by hotrecrystallization in aqueous alkaline silicate might also be transformedinto offretite by dispersion in the specified potassium tetramethylammonium trisilicate solution.

In synthesizing zeolite from mixtures of alkaline materials,conventional practice has been to include significant proportions ofsodium hydroxide in the nutrient even when modifying amounts of asuitable quaternary ammonium hydroxide and/or inorganic hydroxide wasemployed. The present invention features a departure from such practiceby excluding significant proportions of sodium hydroxide from thenutrient and controlling the desired synthesis by the potassiumtetramethyl ammonium trisilicate concentration. Minor amounts of sodium,such as derived from the perlite, do not prevent the operativeness ofthe offretite synthesis. Various modifications of the invention arepossible without departing from the scope of the claims.

The invention claimed is: 1. The method of preparing a catalyticallyuseful composition comprising offretite in an inorganic support whichmethod includes the steps of:

preparing an aqueous nutrient containing potassium hydroxide andtetramethyl ammonium hydroxide as the total alkali, and a mixture ofcalcined minerals selected from the group consisting of expanded perliteand sorptive silica, de-exothermed kaolin and sorptive silica, and metakaolin and sorptive silica, the molar unit ratio of SiO lAl O in saidnutrient being within a range from about 18 to 24, and the molar unitratio of total alkali to alumina in such nutrient being within a rangefrom about 14 to 20;

subjecting said nutrient to aging at a temperature within a range fromabout C. to about C. for from about 1 to about 3 days;

filtering the thus aged nutrient to recover a crude offretitecomposition; and

washing and purifying said offretite composition.

2. The method of claim 1 in which the molar unit ratio of potassiumhydroxide to tetramethyl ammonium hydroxide is within a range from about2.0 to about 2.8.

3. The method of claim 2 in which the unit mol ratio of water to totalalkali is from about 12 to about l8.

# i i Q i

2. The method of claim 1 in which the molar unit ratio of potassiumhydroxide to tetramethyl ammonium hydroxide is within a range from about2.0 to about 2.8.
 3. The method of claim 2 in which the unit mol ratioof water to total alkali is from about 12 to about 18.